The realistic limits on wind power are probably much lower than scientists have suggested, according to new research, so much so that the ability of wind turbines to have any serious impact on energy policy may well be in doubt. Even if money were no object, the human race would hit Peak Wind output at a much lower level than has previously been thought.

This new and gloomy analysis for global wind power comes from Professor David Keith of the Harvard School of Engineering and Applied Sciences. The prof and his collaborator, Professor Amanda Adams of North Carolina uni, have weighed into a row which has been taking place for some years between crusading pro-wind physicists and their critics.

The pro-wind boffins, led by such figures as Harvard enviro-prof Michael McElroy and Mark Jacobson of Stanford, have long contended that if there is any upper limit on the amount of energy that could be extracted from the Earth's winds it is well above the amount the human race requires. They further contend that extracting these vast amounts of power from the atmosphere will not have any serious impact on the world's climate.

Both these assertions, however, have been called into doubt - and the first one, that there's plenty of wind power to meet all human demands, is particularly shaky as it ignores the thorny issue of cost. McElroy, Jacobson and their allies tend to make wild assumptions - for instance that it would be feasible to distribute massive wind turbines across most or even all of the planet's surface.

Professor Keith has some scathing criticism for these ideas. To start with, he says that most large-scale wind potential calculations thus far have simply ignored the problem that the possible massive wind farms of the future are going to result in much less powerful winds for long distances behind them. He and Professor Adams write:

Estimates of global wind resource that ignore the impact of wind turbines on slowing the winds may substantially overestimate the total resource. In particular, the results from three studies that estimated wind power capacities of 56, 72 and 148 TW respectively appear to be substantial overestimates given the comparison between model results and the assumptions these studies made about power production densities ... To cite a specific example, Archer and Jacobson assumed a power production density of 4.3 W m-2 ... production densities are not likely to substantially exceed 1 W m-2 implying that Archer and Jacobson may overestimate capacity by roughly a factor of four.

Peak Wind

Keith and Adams are referring to Archer and Jacobson's paper last year [1], in which they suggested that a "practical" windpower system of the future - employing 4 million wind towers spread all round the world to avoid damage to the environment (!) - might yield average output of 7.5 terawatts over time.

Professor David Keith.

As we pointed out at the time - we not being top physicists here at the Reg, but at least knowing what a Watt is - this is actually far less energy than the human race now requires, and wildly less than the amount of energy it would require if it were to build and maintain a colossal worldwide grid of enormous steel and carbon towers sunk into heavy concrete foundations along with the necessary associated world-spanning interconnectors, grid extensions, transport access into remote wilderness etc etc.
Harvard uni now informs us:

Keith’s research has shown that the generating capacity of very large wind power installations (larger than 100 square kilometers) may peak at between 0.5 and 1 watts per square meter.

As opposed to the 4+ watts assumed by Archer and Jacobson. In other words we'll be hitting Peak Wind a lot sooner than anyone thought. Archer and Jacobson's ridiculous unbuildable world wind project - which seemed likely to cost substantially more than the entire human race's economic output - would actually produce as little as one-eighth of what they think: and that was only a quarter of the amount of power that the human race might reasonably ask for (ie, say two-thirds of what a present-day European uses for everyone). So it would be able to provide about 3 per cent of global energy requirements, or well under a terawatt.
And we have to bear in mind that in the real world things are much worse still for windy dreams. Professors Keith and Adams go on:

Total wind power capacity can — of course — be very large if one assumes that turbines are placed over the entire land surface or even over the land and ocean surface, but while these geophysical limits are scientifically interesting their relevance to energy policy is unclear.

More policy-driven wind power capacity estimates have restricted the area considered ... Yet these estimates have used power production densities that are several times larger than the wind power production limit of around 1 W m-2 ... It is therefore plausible that wind power capacity may be limited to an extent that is relevant to energy policy.

It should be made clear that Professor Keith is starting from the position that global warming is still definitely on (at some point, it has been stalled for well over a decade) and that humanity must go carbon-free or anyway carbon-very-low within a lifetime, generating "several tens of terawatts" of low to nil-carbon power on that timescale. The professor is merely pointing out that wind certainly can't do anything like the whole job in that scenario, and it may not actually be able to do very much at all.
“It’s worth asking about the scalability of each potential energy source," says the prof, "whether it can supply, say, 3 terawatts, which would be 10 percent of our global energy need, or whether it’s more like 0.3 terawatts and 1 percent."

It's definitely looking as though we would be hitting Peak Wind down at the low end of that range. And with wind very much the poster child of renewable power - it is cheap, scalable and practical compared to the other methods - that would seem to be the effective end for the dream of a renewables-powered future for humanity.

This study errs in its assessment of potential wind energy resources by ignoring real-world data and experience and instead relying on crude theoretical modeling techniques. In reality, wind project developers and investors work closely with atmospheric scientists and other experts to make sure that their projects will produce as much as expected, and real-world data from large-scale wind installations in the US and Europe confirms that they do. Regardless of who is correct, the inescapable fact is that America's developable wind energy resources are many times greater than our country's energy needs.

For more, see:http://www.awea.org/blog/index.cfm?customel_dataPageID_1699=21714